Composition for metal plating of plastics

ABSTRACT

PLASTIC SURFACES ARE PREPARED TO MAKE THEM SUSCEPTIBLE TO BEING PLATED BY CHEMICAL PLATING SOLUTIONS BY TREATMENT WITH A SOLUTION OF A NOBLE METAL SALT, FOR EXAMPLE, PALLADIUM CHLORIDE, IN AN ACID ETCHANT FOR THE PLASTIC, FOLLOWED BY TREATMENT WITH A SOLUTION CONTAINING AMINE BORANES OR AMMONIA BORANE. THE BORANE SOLUTION MAY BE A CHEMICAL PLATING SOLUTION, IN WHICH CASE, THE SECOND STEP OF THE SURFACE PREPARATION AND THE PLATING OCCURS SIMULTANEOUSLY.

United States Patent Office 3,661,783 Patented May 9, 1972 U.S. Cl. 252-792 3 Claims ABSTRACT OF THE DISCLOSURE Plastic surfaces are prepared to make them susceptible to being plated by chemical plating solutions by treatment with a solution of a noble metal salt, for example, palladium chloride, in an acid etchant for the plastic, followed by treatment with a solution containing amine boranes or ammonia borane. The borane solution may be a chemical plating solution, in which case, the second step of the surface preparation and the plating occurs simultaneously.

I This application is a division of my application Ser. No.

643,053, filed June 2 1967, now U.S. Pat. No. 3,507,681.

This invention relates to the electroless plating of metals on plastics and more particularly to such plating in which the plastic surfacev to be plated is pretreated to make it susceptible to being plated by a chemical plating bath.

The conventional method of forming a metal plate on plastics by electroless or chemical plating, which plate can then be a base for further electroless plating or for electroplating, utilizes, after cleaning to remove soil and grease, a series of sequential surface conditioning treatments: (1) the surface is etched by dipping in an etchant for the particular plastic to roughen or modify the plastic surface to make it receptive to subsequent treatment, (2) the etched surface is sensitized by dipping in an acid solution of stannous chloride, (3) the sensitized surface is activated by dipping in an acid solution of a noble metal chloride, such as palladium chloride. The thus pretreated plastic is then dipped in a chemical plating bath containing metal ions and a reducing material such as hypophosphites or amine boranes. It is conventional to water rinse the surface between each treatment step.

aqueous solution of amine boranes or ammonia borane, in

which case the plastic surface is activated so that it is susceptible to plating with any chemical plating bath. In the now' preferred embodiment the boraue solution is itself an electroless chemical plating bath containing metal ions as well as the borane, in which case, the plastic is directly i plated with the metal corersponding to the metal ion or ions in the bath.

The etchactivator bath of this invention is a solution of a noble metal salt, particularly chlorides such as gold chloride, platinum chloride, or preferably palladium chloride in an etchant for the particular plastic to be treated The etch-activator solution should contain at least about 0.001 weight percent noble metal salt and preferably to obtain high plating rates between about 0.005 and 0.010 weight'percent. The bath may contain higher amounts of noble metal salts, but is generally undesirable because no substantial benefit is realized and the salts are quiteexpensiye. The etchant used, is of course, selected to be effective with the particular plastic to be used and any acid etchant in which the noble metal salts are soluble is satisfactory for use in the etch-activator solutions. Generally, acid etchants are mixtures of oxidizing acid, such as chro mic acid and sulfuric acid mixtures formed by dissolving chromic oxide or alkali metal chromates in sulfuric acid. Phosphoric acids are also commonly used as etchants in admixture with chromic acid and sulfuric acid. The echants may also contain adidtives such as, for example. wetting agents. In addition, there are a number of acid proprietary etchants which may also be used in making the pretreatment bath of this invention, provided, of course, that the noble metal salt can be dissolved therein. Any plastic that is etched by acid etchants, such as ABS (acrylonitrile-butadieneastyrene copolymers) and polystyrene, and acetates and polyolefins that are etchable with acid etchants after pretreatment with organic solvents.

The conditions of treatment with the etch-activator solution such as temperature and time of contact, may be varied widely depending on the particular etchant and plastic used. Conditions at which the etchant alone will satisfactorily etch the plastic are suitable conditions for use of the etch-activator bath. Generally, a slightly elevated temperature, between about 40 and C., and a contact time of about 1 to 10 minutes are used.

Following treatment with the etch-activator, the plastic surface is contacted with a solution containing an amine boraue or ammonia borane. This may suitably be essentially a solution of the boraue in an inert solvent, suitably water, preferably containing between about 0.01 and 1 moles/liter of amine borane or ammonia borane. Higher concentrations of boranes may be used if desirable without detriment or benefit. The amine borane may be any of the wide variety of amine boranes used in electroless plating baths, such as boranes of primary, secondary and tertiary amines. In such instances the surface is activated so that any metal or alloy electroless plating solution will form an adherent plate on the surface by conventional methods, regardless of the reductant used in the plating baths. For example, nickel plates may be laid down from conventional hypophosphitenickel plating solutions and copper from conventional formaldehydecopper plating solutions.

Preferably the boraue-containing solution is 'itself an electroless plating bath. Bol'ane chemical plating baths contain an amine boraue or ammonia borane and a soluble metal salt, such as nickel, cobalt, iron or zinc salts, and, if desired, additional solubilizing agents, chelating agents, stabilizers, buffering materials or other additives. A large number of such plating baths are well known, such as those disclosed by Hoke in U.S. Pat. 2,990,296, by Zirngiebl and Klein in U.S. Pats. 3,140,188 and 3,234,031, by McLeod in U.S. Pat. 3,062,666, and by E. I. du Pont de Nemours and Comany in British Pat. 842,826. Any of the electroless plating baths with an amine borane reductant, such as boranes of primary, secondary or tertiary amines, as well as ammonia borane, may be used in the practice of this invention. The preferred reductant is dimethylamine borane, as baths having this reductant give complete coverage of the surface at a somewhat faster rate than those containing only other amine boranes. Generally, the concentration of amine borane in such plating baths is between about 0.01 mol and 0.1 mol per liter, the concentration of metal ion is between about 0.02 mol and 0.3 mol per liter, and the pH is maintained above about 3.5. When borane plating solutions are so used an adherent continuous metal plate, corresponding to the metal ion in the solution, is

the plating bath is ordinarilyuseable.

The borane solution may' be a plating solution having primarily another chemical reductant and only. a small catalytioamountiofamine borane or ammonia borane.

For example, avnickel plate is formed when a plastic surface pretreated withetch-activatoris contacted with a conventionalhypophosphite-nickel 7 (bath containing as little as 0.001 mol/liter of amine borane or ammonia borane. I It should be recognized that the metal plates may be single metals or alloys, depending on the plating bath and conditions used, and frequently will contain minor amounts of boron or phosphorous. This invention is applicable for use with any of the well-known chemical plating baths and such bath compositions or plates produced therefrom constitute no part of my discovery.

The following examples are illustrative of this invention.

EXAMPLE I A placque of ABS plastic Cycolac EP-3510 (Marbon Chemical Company) was cleaned by a dip in an alkaline cleaning solution to remove extraneous dirt and grease. The placque was then immersed for two minutes at 50 C. in an etch-activator bath containing 100 g. Cr O 50 ml. of concentrated H 80 0.0221 g. of PdCl and sufiicient water to bring the solution volume to 400 ml. The placque was then rinsed with water and immersed for 2 minutes at 50 C. in a chemical plating bath having the following composition: NiS'O '6H O, 0.13 mol/liter; C H -H O, 0.07 mol/liter, (CH NBH 0.04 mol/ liter; and NH OH to pH 7.0-7.5. At the end of the treatment, the placque was covered with a continuous adherent, bright nickel plate.

EXAMPLE II Example I was repeated, except the etch-activator was (a) diluted to /2 the original concentration, (b) 25 ml. of concentrated H 80 was added to the etch-activator, and (c) 250 ml. of 72 wt. percent H 80 was added to the etch-activator, with substantially the same results.

EXAMPLE III A clear placque of Cycolac EP-35 10 was immersed for 4 minutes at 60 C. in an etch-activator bath containing 30 g. of Kzcl'goq, 200 ml. of concentrated H 80 0.1096 g. 'PdCl and 200 ml. of water. After rinsing with water, the placque was plated with nickel as in Example 1.

EXAMPLE IV Example I was repeated with the same results, except that the etch-activator contained 0.0067 g. of PdCl EXAMPLE V Example HI was repeated using etch-activator solution to which 10, 20, 30 and 40 ml., respectively, of 85% H PO was added. The plating rate was slightly faster than Example 1V in the first three'runs and somewhat slower in the fourth run.

EXAMPLE VI A placque of Cyclolac-EP-35'10 was immersed for two minutes at 60 C. inan etch-activator bath containing 200 ml. concentrated H 80 25 ml. concentrated HCl, 0.1255

then each was nickel plated with various amine borane.

chemical plating baths. A number of placques were satissformedontheplastic surface under..the conditions which factorilyplated. with baths. containing dimethylamine borane and nickel sulfate, the concentration of dimethylamine borane ranging from 2.0 g./l. to 3.5 g./l., the pH ranging from 5.0 to 9.0, and with various nickel complexing agents, including'citrates, lact-ates, glycolates and ammonia,1iat temperatures between "about 30fl C. and 65 C. p

A pretreated placque was satisfactorilyrplated- 1at-=-50 C. with a bathcontaining 7.5 g. of NiSO4-6H O, 5 g. of citric acid dihydrate, 0.3 g; Nl-l B-Hgfwaterto"'25 0 ml: total volume, and NH OH to a"pH of"6.5. I v

Another pretreated placque was sa" factorily plated at 65 C. with a bath containing 15 g. NiSO;-6H O', 10 g. of citric acid dihydrate, 5 g. tributylamine borane, water to 400 ml. total volume, and NH OH to a pH of EXAMPLE VIII To illustrate the unsuitability of plating baths containing only hypophosphite reductan-ts, a, placque pre treated as in Example IV was immersed at 65 C. in a hypophosphite bath containing 8.1 g. NiSO -6H O, 12.8 g. of lactic acid, 4.0 g. succinic acid, 9.6; g. NaH PO water to 400 ml. total volume, and NaOH to a pH of 5.5. Therewas negligiblenickel deposition, even when placques had been immersed as-long as 60 minutes in the etch-activator bath and in the hypophos phite plating bath. The hypophosphite bath is a typical bath that produced good plates on plastics pr'etreated by the prior art procedures outlined hereinbefore. i EXAMPLE IX Example VIII was repeated except that 0.12 g. of di-, methylamine borane was added to the. hypophosphite. bath and a good nickelplate was produced with an immersion time of two minutes in the etch-activator;

5-10 minutes in the plating bath. I .7

EXAMPLE X A placque pretreated as in Example IV was imf mersed in a 1 wt. percent aqueous dimethyla minebor; ane solution and rinsed with water. A good nickel plate was formed when the placque was immersed in the hypo phosphite bath of Example VIII.

EXAMPLE XI I about 0.001 and 0.01 wt. percent of a noble metal salt in an etchant selected from the group co'nsistingof -mix-- tures of chromic and sulfuric acids andmixtures thereof withphosphoric acid'w' r 7 2. A bath according to claimnl in which the salt is palladium chloride.

3. A bath according-to claim. 2 containing between about 0.005 and 0.10 wt. percent salt.

References Cited s I, UNITED STATES; PATENTS 3,445,350 5/1969 Klinger a 'ai t 2 04536 JACOB H. SDEINBERG, Primary Examiner US. :1. X.R. e 101-1; 117-47 R; 148--6.14; 1562; 204--38' 

